Method of burning sewer pipe and the like



Nov. 17, 1959 A. L. BEN

NETT 2,912,741

METHOD OF BURNING SEWER PIPE AND THE LIKE Filed April 5, 1957 ll 1 i U-'."VENTOR. 1445527 555 BEAM/Err;

I BY

I I W 4044 namely,

United States Patent Office 2,912,741 Patented Nov. 17, 1959 METHOD OF BURNING SEWER PIPE AND THE LIKE Albert Lee Bennett, Glendale, Calif., assignor to Pacific Clay Products, Los Angeles, Calif., a corporation of California Application April 5, 1957, Serial No. 650,951

10 Claims. (Cl. 25157) This invention pertains to a method of rapidly firing tubular, ceramic composition objects to uniform size and maturity and is particularly d.rected to a method of efficiently and rapidly burning formed sewer pipe.

Although the invention is applicable to the burning of any hollow, tubular, ceramic composition object, such as, for example, pipe, conduit, high-temperature resistant cores and resistance elements muflie furnaces and the like, etc., the description given hereinafter will be particularly directed to the application of the methods of this invention to the production of sewer pipe, such example permitting those skilled in the art to apply the teachings hereof to the manufacture of other tubular, ceramic composition products. Moreover, although sewer pipe, drain pipe and the Lke are generally formed from clay bodies, which may or may not contain aggregate or grog and in which the clay may differ in plasticity, open burning characteristics, shrinkage, etc., the invention is not limited to any particular composition, since tubular objects made from compositions containing a relatively low percentage of clay and high in talc, magnesia and other ceramic raw materials may also be employed, depending upon the ultimate use to which the burned object is to be put. Moreover, it is to be noted that the method of the present invention is capable of being carried out in many different types and arrangements of equipment. The exemplary form of apparatus described hereinafter is therefore illustrative of only one form of apparatus in which the method may be carried out and is not limited thereto.

Sewer pipe and drain pipe may be either formed with plain ends or with the well-known bell and spigot ends, and as previously indicated, may be made from a variety of clay compositions, those skilled in the art being familiar with the manner of preparing theraw materials, blending the ingredients and forming such pipe by Wellknown apparatus, such as for example, a sewer pipe press or extrusion machine, or auger. Although heretofore sewer pipe and drain pipe have been made in relatively short lengths, say three feet, the method of the present invention is also applicable to the manufacture of longer lengths, say six foot lengths of such pipe.

Ordinarily, the manufacturing operations comprise forming, drying, and then subjecting the pipe to a firing operation which may be said to comprise three stages, water-smoking, oxidation, and vitrification. Drying may be said to comprise mechanical dehydration or the removal of mechanically held water and occurs at temperatures below 300400 P. Water-smoking may be said to comprise chemical dehydration or the removal of chemically held water and generally takes place at temperatures of between about 350 F. and 1000" F. Oxidation of the components of the body may take place at temperatures of from about 700 F. to as high as 1700 F. and vitrification can be observed at temperatures as low at 1600 F. and proceeds until incipient fusion and fusion are attained. Different clay compositions containing different clays, grog, fluxes, etc.

behave differently and the ranges given for the various eflects overlap to a considerable extent.

The firing or burning operation is carried out to attain a desired maturity in the formed article evidenced by a desired degree of vitrification and reduced porosity or absorption characteristics, the development of adequate strength, etc. Seger cones are usually used to indicate maturity or degree of vitrification obtained by burning ceramic compositions and are based upon the time-temperature relation normally employed in burning ceramic objects, that is, a heating rate of 20 C. (approximately 35 F.) per hour up to end points on the order of 2700 F.

In contradistinction, the heating or firing methods of ths invention contemplate the use of heating rates of over 200 F. per hour and as high as 850 F. per hour. Such extraordinary, rapid heating rates have not been considered in the past; the alpha, beta, tridymite and cristobalite inversions of quartz and silica (which occur in substantially all clays and ceramic compositions) and the volumetric changes and stresses which accompany such inversions were deemed heretofore to necessitate slow heating and cooling rates to prevent cracking, spalling, checking and other evidence of imperfect or useless burned products.

By the use of the extremely rapid heating rates contemplated by this invention ceramic objects can be burned to maturity within a remarkably short period of time. Whereas a periodic kiln requires at least 4 to 5 days and often as long as 10 days to complete a burn and a tunnel kiln requires 24 to 36 hours, the present method permits a burn to be completed in about 200 minutes or 3 to 3 /2 hours. Moreover, a tunnel 'kiln entails an initial cost of about twice the cost of an installation arranged to produce an equivalent amount of pipe pursuant to the present'method. These economical advantages accrue in addition to the improved quality of the products made in accordance with the present invention.

It has been discovered that the inversions of silica can be disregarded and extremely high heating rates utilized, provided the fuel and air are supplied in a particular manner to the ware. When the fuel and air are properly applied, uniform heating of the ware takes place and products of remarkable uniformity with commercially insignificant losses can be obtained.

Generally stated, the method of the present invention contemplates the positioning of a plurality of tubular, hollow, unburned, ceramic composition objects in adjacent relation with their axes substantially parallel and vertical upon a supporting surface and then supplying fuel and air to the lower, inner portion of each of said objects so as to form an elongated flame and rapid, upward passage of gas through each of the objects. In this manner the objects are uniformly heated. During burning the supply of fuel is rapidly increased to thereby increase the temperature in the firing zone and of the objects at a rate of between 40 F. and F. per 10 minutes during the firing period, whereby vitrification of at least cone 02 is obtained in less than 4 hours.

It is an object of the present invention, therefore, to disclose and provide a method of burning hollow, tubular objects formed from ceramic compositions in a uniform and rapid manner.

A further object of the present invention is to disclose and provide conditions and rates whereby the production of commercially satisfactory, well burned, tubular ceramic objects, such as sewer pipe, can be greatly accelerated.

These and other objects and advantages and details as to procedure to be employed will appear from the following description wherein, .for purposes of illustration and as a means of comprehension, reference will be had to the appended drawings, wherein:

Fig. 1 is a diagrammatic representation of an arrangement of elements in which the method may be carried out.

Fig. 2 is an enlarged fragmentary view, partly broken away, illustrating one method of positioning and supplying heat to tubular objects in a firing zone pursuant to the teachings of this invention.

Fig. 1 shows a stationary supporting surface It preferably made of refractory material upon which a plurality of unburned, tubular, ceramic composition objects, such as the sewer pipe 20, are supported. The kiln 2 may comprise side walls 3 and 4 and a roof 5, the ends of this kiln being open but provided with movable end doors such as 6 and '7. The kiln 2 may be movable along tracks 8-8 into position so as to en close the stationary supporting floor 1. During firing the end walls 6 and 7 are moved into position to close the open ends of the kiln 2, thereby forming a firing chamber or zone. The kiln may be provided with a suitable hood 9, passages for heated gases, outlet to a stack, bafiies to divert gases to other areas of the plant whereby waste heat may be utilized for drying, suitable circulating fans for facilitating the flow of such gases, etc. These details of construction are not illustrated since the provision of adequate stack openings, methods of recirculating hot gases, and the use of vanes and ducts to divert heated gases to other zones used for drying, etc., do not form a part of the present invention and can be supplied by ceramic engineers.

By referring to Fig. 2, it will be noted that the stationary supporting surface 1 is provided with a plurality of openings, such as ill, 12 and the like. Within each opening there is positioned a suitable burner, such as the burner 13, operably connected as by means of pipe 14 having a control valve 15 to a manifold 16 leading to a supply of fuel. Each tubular object, such as the sewer pipe 20, is positioned above a burner in its aperture so that the various lengths of unburned sewer pipe, such as 20, 21 and 22, are supported upon the supporting surface or slab 1 in parallel, substantially vertical relation. It has been found desirable, in manufacturing sewer pipe by the method of this invention, that the sewer pipe be out of contact with each other but spaced not exceeding twice the maximum diameter of the pipe. The pipe may be supported directly upon the supporting surface 1 or fixtures or stools such as the cylindrical stools 17 may be provided. Such stools may be provided with ports, such as 13, for the purpose of facilitating the circulation of heated gases throughout the firing chamber. Although in Fig. 2 bell-end pipe is illustrated and each length of pipe is supported with bell end down, it is to be understood that the pipe may be reversed and supported upon a suitable stool with the bell end up. Similarly, plain-end pipe or any other hollow, tubular ceramic object may be positioned upon the floor 1 by the use of a stool or fixture adapted to hold the object in a sub stantially vertical or upright position above its individual heating zone.

When extremely long pieces of pipe are burned it may be desirable to link the upper ends together by means of fixtures such as are illustrated at 9.9, such fixtures stabilizing the entire assemblage of pipe. Other methods or racking means may be used fo the purpose of preventing the pipe from falling, collapsing or contacting.

After the various unburned pieces have been positioned and supported upon the slab in the manner in dicated and the doors to the firing chamber have been closed, fuel and air are supplied to the various burners. Aspirating types of burners are preferred in order to insure adequate oxidizing conditions and the production of a relatively long flame within each tubular object or pipe. Since each burner is surrounded by its air port and each pipe is positioned directly above each burner, the fuel and air are supplied to the interior of each pipe in a direction virtually coaxial with the axis of the pipe. By the use of the control valves 15, the supply of fuel to the burners is readily controlled; when natural or artifical gas is used as a fuel, such valves as well as pressure regulators permit careful control of fuel supplied to the burners. After all of the burners have been lit, the supply of fuel is rapidly increased so as to increase the temperature in the firing zone and of the various pipe arranged therein at a rate of between about 40 F. and 14-0 F. per 10 minutes. The total burning time will, of course, depend upon the maximum temperature to which the objects are to be burned. Control cones placed at various elevations throughout the chamber may be observed to positively determine the end of the firing period. The rapid rate at which heat is supplied to the pipe permits maturity of at least cone 02 in less than 4 hours.

By reason of the fact that heat is supplied to the lower, inner portion of each of the tubular objects, coupled with the fact that air is supplied around each burner and circulation is facilitated by ports 18 in the stools 17, the entire length of the cylindrical or tubular object is uniformly heated. As the temperatures increase, each tubular object radiates heat to its neighbors. Violent circulation of heated gases takes place throughout the heating chamber and it has been discovered that substantially uniform temperature conditions exist in all parts of the chamber.

Adjacent the ends of the supporting floor 1 (and in some instances along the sides of the slab ll) additional openings, such as 11 provided with additional burners such as 33, may be provided, these burners being directed along the refractory inner faces of the end closures, such as 6, or the side walls 3 and 4 of the kiln. These inner surfaces of the kiln are therefore caused to act as sources of radiant heat and further insure the production of uniformly burned objects throughout the kiln.

The rapid rate at which heat is supplied to the pipe virtually eliminates any so-called water-smoking period. In many instances it is desirable to utilize the waste heat of a kiln (made available during the cooling period) to dry freshly formed pipe. A secondary slab or supporting platform can therefore be positioned at another position along the track 88 and while a cooling step is being performed in the kiln while it is in position over slab 1, the waste heat may be used to dry the pipe on the other supporting surface or floor. At the conclusion of such cooling period the entire kiln 2 may then be moved into position over the other slab to conduct another burning operation while pipe is removed from slab 1, new unburned pipe positioned thereon and made ready to be dried by the waste heat at the conclusion of the second burning o eration on the second slab or platform.

The method of the present invention permits sewer pipe to be burned with amazing rapidity. For example, predried pipe positioned in the manner disclosed and having a temperature of about 500 F. at the start of a burning operation have been burned to a maximum temperature of 2100 F. in a period of 140 minutes. A temperature of 1040 F. was reached in 30 minutes; 1450 F. in 60 minutes; 1780 F. in minutes; 2020 F. in minutes and 2100 F. in minutes, whereupon the supply of fuel was discontinued, and the residual heat in the pipe then utilized for drying the next batch of pipe. The cooling of the pipe burned to 2100 F. was extremely rapid, the temperature dropping to 1400 F. within 10 minutes after the firing was discontinued, to 900 F. in 20 minutes and to 460 F. in 60 minutes. The total burning and cooling period therefore consumed 200 minutes. The 4 in. diameter, 4 ft. long, bell-end sewer pipe burned were in excellent condition with no visible faults or any imperfections capable of being determined during subsequent testing. Their absorption was on the order of 5%. In the exemplary burn just described, natural gas was used as fuel and the pressure of the gas supplied to the burners ranged from A1 oz. water pressure at the beginning of the burn, to 2 oz. at minutes, 3 oz. at 50 minutes and 4 oz. at 80 minutes. The gas supplied to the burners at the radiant walls was at somewhat higher pressures. All flames generated were substantially as long as the lengths of the pipe toward the end of the burning period.

I claim:

1. In a process of making clay body sewer pipe, the steps of: supplying fuel and air to the lower, inner end portion of each of a plurality of unburned sewer pipe positioned upon a supporting surface in adjacent relation with axes substantially parallel, said fuel and air being supplied in a direction coaxial with the axis of the pipe and in proximity to the end of the pipe to produce a combustion flame within said pipe and rapidly increasing the supply of fuel to thereby increase the temperature of the pipe at a rate of between 40 F. and 140 F. per each 10 minutes during a firing period, whereby vitrification of at least cone 02 may be obtained in less than 4 hours.

2. A process as stated in claim 1, wherein the sewer pipe are exposed to radiant heat concurrently with the supply of fuel and heat to the inner end portions thereof.

3. In a process of rapidly firing tubular hollow ceramic composition objects such as clay pipe the steps of: positioning a plurality of formed tubular unburned ceramic composition objects in adjacent relation with their axes substantially parallel upon a stationary supporting surface; enclosing said positioned objects and supporting surface to form a firing zone; supplying fuel and air to the lower inner end portion of each of such plurality of unburned objects in a direction parallel to the axis of such objects to form a combustion flame within the objects and rapidly increasing the supply of fuel to thereby increase the temperature of the objects at a rate of between 40 F. and 140 F. per each 10 minutes during a firing period.

4. A process as stated in claim 3 wherein each object is positioned upon a laterally ported support carried by the supporting surface, whereby gases from between said objects pass into the lower and inner portion of said objects.

5. A method of rapidly firing tubular ceramic composition objects to uniform size and maturity comprising: drying formed unburned ceramic objects to remove a portion at least of mechanically held moisture; positioning a plurality of tubular unburned clay body ceramic objects in adjacent relation upon a supporting surface; supplying fuel and air to the lower inner portion of each of such plurality of unburned tubular ceramic objects in a direction virtually coaxial with the axis of each object, said air being supplied in quantity sufficient to insure oxidizing conditions and the production of a long flame within each object; igniting said fuel and air to form such flame within each object and rapidly increasing the supply of fuel so supplied to thereby increase the temperature of the objects at a rate of between 40 F. and 140 F. per 10 minutes during a firing period.

6. A process as stated in claim 5 wherein said tubular objects are positioned out of contact with each other 6 and spaced a distance not exceeding twice the maximum diameter of said objects whereby said objects may effectively radiate heat to each other during firing.

7. In a process of rapidly firing tubular hollow ceramic composition objects such as clay pipe, the steps of: positioning a plurality of formed tubular unburned ceramic composition objects in vertical position and in adjacent relation with their axes substantially parallel upon a stationary supporting surface; moving a refractory insulated hood over said assembly of objects positioned on said supporting surface to form a firing zone; supplying fuel and air to the lower inner end portion of each of such plurality of tubular objects in a direction virtually coaxial with the axis of each object, said air being supplied in quantity suflicient to insure oxidizing conditions and the production of a long flame within each object; and igniting said fuel and air to form such flame within each object and rapidly increasing the supply of fuel to increase the temperature of the objects at a rate of between 40 F. and 140 F. per each 10 minutes during a firing period, whereby maturity of such ceramic objects of at least cone 02 is attained in less than four hours.

8. A process as stated in claim 7 wherein each object is positioned upon a laterally ported support carried by the supporting surface whereby gases from between said objects pass into the lower and inner portion of said objects.

9. A process as stated in claim 7 wherein said objects are out of contact with each other and spaced a distance not exceeding twice the maximum diameter of said objects, and said objects are exposed to radiant heat concurrently with the supply of fuel and heat to the inner end portions thereof.

10. In a process of rapidly firing clay body sewer pipe, the steps of: positioning a plurality of formed, tubular, unburned sewer pipe in adjacent relation with their axes substantially parallel and vertical upon a supporting surface in a firing zone, said pipe being out of contact with each other and spaced a distance not exceeding twice the maximum diameter of said pipe; supplying fuel and air to the lower inner portion of each of said pipe, igniting said fuel and air to form an elongated combustion flame within each pipe, passing heated gases discharged from the upper portion of the pipe from between said pipe into the lower and inner end portions of said pipe, and rapidly increasing the supply of fuel and air to thereby increase the temperature of the pipe at a rate of between 40 F. and F. per ten minutes during a firing period to burn said pipe to maturity.

References Cited in the file of this patent UNITED STATES PATENTS 1,675,735 Stohr July 3, 1928 1,891,764 Henderson Dec. 20, 1932 2,307,322 Ladd Jan. 5, 1943 2,624,930 Weingrad J an. 13, 1953 2,772,082 Hortvet Nov. 27, 1956 FOREIGN PATENTS 5,722 Great Britain Mar. 10, 1909 

